Fibrinogen (Fg) and fibrin (Fb) are hydrolyzed by the blood enzyme, plasmin, in pathological fibrinogenolysis and fibrinolysis. Plasma concentrations of Fg and/or Fb degradation products (FDP) are thus augmented. Since abnormal quantities in plasma indicate that the hemostatic equilibrium is disturbed, a rapid and accurate measure of FDP would be clinically valuable. Human Fg will be degraded by plasmin to fragments Fg-D and Fg-E which are separable by Pevikon block electrophoresis. Soluble, noncross-linked Fb will be similarly digested to Fb-D and Fb-E. Rabbit anti-Fg-E and anti-Fb-E antisera will be absorbed by passage through immunosorbent columns coupled with Fg and normal serum, so that they contain only those antibodies directed against the neoantigen of Fg-E and Fb-E, respectively. The two main radioimmunoassay procedures, (1) double antibody technique and (2) solid-phase immunoassay, will be developed for FDP in plasma based on the neoantigenic expression of Fg-E and Fb-E, respectively. Attempts will be made to produce antibodies specificonly to Fb-E fragment by using the principle of immunological tolerance. Tolerance will be induced in rabbits to Fg-E. Then, rabbits will be hyperimmunized with Fb-E in order to produce antibodies capable of detecting "hypercoagulable states." The FDP levels of patients within the broad categories of obstetrical complications and cardiovascular diseases will be assayed. It is hoped that radioimmunoassay of hypercoagulable states may help unravel the pathogenic mechanism of hemostatic dysfunctions.